In recent years, there has been used an ink jet type liquid jet head for discharging ink droplets on recording paper or the like to render a character or graphics or for discharging a liquid material on a surface of an element substrate to form a pattern of a functional thin film. In such a liquid jet head, ink or a liquid material is supplied from a liquid tank via a supply tube to the liquid jet head, the ink is caused to fill minute space formed in the liquid jet head, and the capacity of the minute space is momentarily reduced according to a drive signal to discharge a liquid droplet from a nozzle which communicates to a groove.
FIG. 12 is an exploded perspective view of an ink jet head 50 of this type. FIG. 13A is a top view of the ink jet head 50, FIG. 13B is a sectional view taken along the line YY of FIG. 13A, and FIG. 13C is an explanatory diagram illustrating a connection structure between wiring electrodes 64 on a flexible substrate 61 and lead-out electrodes 62. The ink jet head 50 includes a piezoelectric substrate 51 having a plurality of narrow grooves 55 formed in a surface thereof, a cover plate 56 having a manifold 57 and a recessed portion 58 formed therein for supplying ink to the grooves 55, a nozzle plate 59 having nozzles 60 formed therein for discharging ink, and the flexible substrate 61 for supplying a drive signal to the piezoelectric substrate 51.
The grooves 55 are formed from a front end 52 to some midpoint between the front end 52 and a rear end 53. The plurality of grooves 55 are separated from one another by side walls 54. The nozzles 60 in the nozzle plate 59 communicate to channels formed by the grooves 55 and the cover plate 56, respectively. The side walls 54 are made of a piezoelectric material and undergo in advance polarization treatment in a vertical direction. Side wall electrodes 63 are formed on wall surfaces of the side walls 54 and are electrically connected to the lead-out electrodes 62 formed on a surface of the piezoelectric substrate 51 on the rear end 53 side. The flexible substrate 61 is bonded to a top surface of the piezoelectric substrate 51 on the rear end 53 side. This allows a drive signal generated in an external circuit (not shown) to be transmitted via the wiring electrodes 64 formed on the flexible substrate 61 and the lead-out electrodes 62 to the side wall electrodes 63 formed on the wall surfaces of the side walls 54. This may cause the side walls 54 to be subjected to shear deformation.
The ink jet head 50 is driven as follows. First, ink is supplied to the manifold 57. The ink is supplied from the manifold 57 and the recessed portion 58 to the respective grooves 55 to fill the channels formed by the cover plate 56 and the grooves 55, respectively. When a drive signal generated in an external circuit is applied via the wiring electrodes 64 formed on the flexible substrate 61 and the lead-out electrodes 62 to the side wall electrodes 63, the side walls 54 are subjected to shear deformation to reduce the capacity of the channels, thereby discharging from the nozzles 60 ink which fills the channels.
Japanese Patent Application Laid-open No. Hei 9-29977 describes an ink jet head which is similar to the above-mentioned ink jet head 50. A plurality of narrow grooves are formed in a surface of a piezoelectric ceramic substrate from a front end thereof to some midpoint between the front end and a rear end thereof, and a lid is bonded so as to cover the plurality of grooves. The lid has ink chambers formed therein for supplying ink to the plurality of grooves, respectively. Piezoelectric side walls for separating the respective grooves from one another have a conductive layer which is formed from upper edges of the side walls to bottom surfaces of the grooves. The conductive layer is routed from a front end which is on a discharge side of the piezoelectric ceramic substrate to a back surface side of the piezoelectric ceramic substrate to be connected to lead-out electrodes formed on the back surface. The plurality of lead-out electrodes on the rear surface are in the form of a fan so that the distances among the plurality of lead-out electrodes become larger from the front end to the rear end of the piezoelectric ceramic substrate. This facilitates connection between the lead-out electrodes and an external circuit.
Japanese Patent Application Laid-open No. 2000-168094 describes an ink jet head in which a plurality of recessed grooves are formed in parallel with one another in a surface of an actuator substrate formed of a piezoelectric body, top surfaces of the recessed grooves are covered with a cover plate, a nozzle plate is bonded to a front end of the actuator substrate, and a plate and a manifold member for supplying ink to a rear end are provided. Channels are formed by the plurality of recessed grooves in the actuator substrate and the cover plate which covers the top surfaces of the grooves. The channels are formed from the front end to the rear end of the actuator substrate. With regard to the plurality of channels, jetting channels for jetting liquid droplets through nozzles in a nozzle plate and dummy channels to which ink is not supplied are alternately arranged. Conductive patterns for driving are formed on wall surfaces of piezoelectric side walls for separating the grooves from one another. The conductive patterns are routed via a side surface of the actuator substrate to a back surface side thereof. This may eliminate the need for forming a rising portion having a predetermined length at the rear of the dummy channels, and the dummy channels may be made shorter, which may reduce the costs of the actuator substrate and, further, may shorten a period of jetting ink.
Japanese Patent Application Laid-open No. 2002-210955 describes an ink jet head in which an ink manifold is provided around a head chip. In the head chip, channels are formed by sandwiching side walls formed of a piezoelectric element between a lower substrate and an upper substrate, and a nozzle plate is formed at one end of the channels while a backplate having ink introduction holes formed therein for introducing ink into the channels is formed at the other end of the channels. An ink manifold member having an ink chamber and an ink flow path formed therein is provided on a rear surface of the backplate. The ink manifold member includes a top surface covering portion which extends out above the upper substrate forming the head chip.
Drive electrodes are formed on wall surfaces of side walls which form the channels, and the drive electrodes are provided so as to extend to top surfaces of the side walls. Electrodes which pierce the upper substrate and which are exposed on a surface of the upper substrate are formed at positions of the upper substrate which correspond to the channels, respectively. Further, electrodes which pierce the top surface covering portion of the ink manifold member in a thickness direction are formed at positions of the top surface covering portion of the ink manifold member which correspond to the electrodes formed in the upper substrate, the electrodes piercing the top surface covering portion being connected to wiring electrodes formed on a top surface of the top surface covering portion, and further, being routed to an outside rear surface of the ink manifold member. As a result, the drive electrodes which are formed on the side walls and are for driving the channels are connected via portions of the top surfaces of the side walls at which the drive electrodes are extendedly provided, the piercing electrodes through the upper substrate, and the piercing electrodes through the top surface covering portion to the wiring electrodes formed on the top surface covering portion and are routed to the rear surface side of the ink manifold member. This enables supply of a drive signal to the drive electrodes from the rear surface side of the ink manifold member, which may facilitate a stacked structure and may simplify a connection structure to a printer main body.
In the ink jet heads illustrated in FIG. 12 and described in Japanese Patent Application Laid-open No. Hei 9-29977, the grooves 55 forming the channels are formed from the front end to before the rear end. The grooves 55 are formed to before the rear end so as to prevent leakage of ink to the rear end side. The grooves 55 are formed by rotating at high speed a dicing blade having a grinding material embedded in an outer peripheral portion thereof, and lowering the blade by a predetermined distance into the surface of the piezoelectric substrate 51, to thereby grind the piezoelectric substrate 51 while moving the blade along the surface of the piezoelectric substrate 51. Therefore, the shape of the ends of the grooves 55 reflects the shape of a segment of a circle of the dicing blade. When the diameter of the dicing blade is 2 inches and the depth of the formed grooves 55 is 360 μm, a length X1 of slanted portions of bottom surfaces of the grooves 55 at the ends is 4 mm or more. A width X2 of the piezoelectric substrate 51 in a direction of the grooves 55 is about 10 mm, and hence the slanted portions occupy about 40% of the whole width. Further, portions of the piezoelectric substrate 51 functioning as actuators which are driven to discharge ink are mainly portions of the side walls 54 corresponding to flat bottom surfaces of the grooves 55. Portions of the side walls 54 corresponding to the above-mentioned slanted portions almost do not function as actuators, and this tendency becomes more prominent as the depth of the grooves 55 becomes smaller. The slanted portions which almost do not function as actuators occupy a considerable proportion of the whole width, which is an obstacle to miniaturization of the ink jet head 50, and to achievement of cost reduction by increasing the number of the piezoelectric substrates which can be manufactured from one wafer.
On the other hand, as described in Japanese Patent Application Laid-open No. 2000-168094 and Japanese Patent Application Laid-open No. 2002-210955, when recessed grooves are formed straight from the front end to the rear end of the surface of the piezoelectric substrate or the actuator substrate, the shape of a segment of a circle of the dicing blade is not reflected and the width of the head may be prevented from increasing due to the slanted portions of the bottom surfaces of the grooves. However, as a tradeoff, formation of the lead-out electrodes for leading to the outside the drive electrodes formed on the side walls is quite complicated. For example, in Japanese Patent Application Laid-open No. 2000-168094, in addition to formation of the recessed grooves for the dummy channels and the jetting channels, vertical grooves and divided grooves which communicate to the dummy channels are formed in the front end surface and the back surface of the actuator substrate. Further, a conductive layer is formed on the whole surface of the actuator substrate by plating or the like, and after that, an excimer laser beam is used to pattern an electrode layer on the dummy channels and an electrode layer on the front end surface, the rear end surface, and the back surface of the actuator substrate, to thereby form the lead-out electrodes. Therefore, the manufacturing method is quite complicated.
Further, in Japanese Patent Application Laid-open No. 2002-210955, the piercing electrodes corresponding to the channels are formed in the upper substrate of the head chip and are electrically connected to the drive electrodes formed on the wall surfaces of the side walls formed of the piezoelectric element, and further, the piercing electrodes corresponding to the channels are also formed in the top surface covering portion located thereabove. Therefore, the manufacturing steps are quite complicated. Further, contact between the electrodes which are formed on the top surfaces of the side walls formed of the piezoelectric element, and the electrodes which are formed in the upper substrate, and contact between the electrodes which are formed in the upper substrate, and the electrodes which are formed in the top surface covering portion are necessary. A lot of contacts are required, and thus, it is quite difficult to ensure the reliability of the contacts.